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Most common is the coolant system may have a air pocket. Since you did drain the coolant system, if the system is not bleed properly, you can get no heat at idle, or no heat, and over heating. Nissan's are tricky when it comes to bleeding the coolant system. Here is the way you need to bleed the coolant system.
To bleed the coolant system, remove the radiator cap. Install the coolant bucket. Fill the bucket about 1/2 way. Then raise the front of the car as high as if it were on ramps. This way if there is air in the coolant system, the circulation brings it to the highest point. Then turn on the car, and put the heat on speed number 4, recirc mode on, and face mode. You may need to rev the engine a few times to move the coolant around to get the air out. After you have good heat, and little to no bubbles in the coolant bucket. Then the coolant system is properly bleed. You should have good heat when bleed properly. So when you put your hand over the vent and hold it there for 30 seconds, you get a slight burning sensation. That is perfect heat.
If you don't have a coolant bucket, you can make one. See image. Just pinch off the over flow hose.
If you have any more questions on this, please feel free to ask. Thanks Jay!